1. Field of the Invention
The present invention relates to a method for fabricating a silicon-on-insulator wafer, particularly to a cost reductive method.
2. Description of the Related Art
According to recent developments in semiconductor fabrication technology to high integrity and fast operation, the semiconductor integration technology employing a silicon-on-insulator wafer, hereinafter "SOI" wafer, instead of employing bulk silicon wafer has been remarkably reported. SOI wafer generally includes a first silicon substrate for supporting the entire structure, a second silicon substrate in which a device are formed and a buried oxide film interposed therebetween are formed. The semiconductor device integrated on the SOI wafer as described above, enables a complete device isolation, a reduction of parasitic capacitance and a fast operation.
The SIMOX (separation by implanted oxygen) method using oxygen ion implantation and bonding method bonding two silicon substrates are frequently used as conventional method for fabricating SOI wafer. In the SIMOX method, oxygen ions are injected into a bulk silicon wafer, and then the oxygen ions and the silicon ions are reacted each other thereby forming a buried oxide film in a selected depth of the wafer so as to isolate the wafer. In the bonding method, an oxide film is formed on one substrate of a first silicon substrate and a second silicon substrate, and then two substrates are bonded each other with sandwiching the oxide film and next, an expected thickness of the second silicon substrate is left behind by polishing the second silicon substrate where a device is to be formed.
However, the SIMOX method for fabricating an SOI wafer carried out by the oxygen ion implantation has disadvantage in that the oxygen ions may cause a crystalline defection of silicon layer and it is difficult to adjust thickness of the silicon layer. Furthermore, this method requires longer fabrication time. Therefore recently the bonding method bonding two substrates is frequently used.
FIGS. 1A to 1D are cross-sectional views for showing a conventional method for fabricating SOI wafer.
Referring to FIG. 1A, a first silicon substrate 10 being comprised of bulk silicon is provided. A first oxide film 11 is formed on the first silicon substrate 10 by a thermal oxidation process.
Referring to FIG. 1B, a second silicon substrate 20 being comprised of bulk silicon is provided. A field oxide film 21 is formed on the second silicon substrate 20 by LOCOS. A second oxide film 22 is deposited on the second silicon substrate 21 in which the field oxide film 21 is formed.
Referring to FIG. 1C, the first silicon substrate 10 and the second silicon substrate 20 are bonded such that first oxide film 11 and the second oxide film 22 are in contact with each other respectively, and are heat-treated so that a selected degree of bonding intensity is given thereto. Referring to FIG. 1D, the backside of the second silicon substrate 20 is polished so that a required thickness of silicon layer is left behind.
This SOI wafer fabricated according to the above processes can be made with ease. Nevertheless, high fabrication cost is the shortcoming of this type of SOI wafer since one SOI wafer is made out of two silicon substrates.